The overall objective is to investigate masses, volumes, flow rates, blood-tissue transport mechanisms and metabolism in mammalian tissues, organs and the whole body by means of the multiple indicator dilution experiment. The proposed work consists of determining (a) the tracer permeability and the reflection coefficient of the lung endothelial and epithelial barriers to several series of lipid-soluble and lipid-insoluble molecules, (b) the filtration coefficient and the tracer permeability of the lung endothelial and epithelial barriers to water, (c) masses, volumes of distribution, and input and output rates of various body substances and carrier fluids in the whole body from tracer kinetic measurements in the plasma, (d) to set up mathematical models of distribution of tracer substances and osmotically active substances passing through tissues, organs and the whole body which relate such measurable quantities of indicator dilution experiments as concentrations of specific activities vs time to independently measurable physiological parameters such as blood flow, volume of distribution, permeability, reflection and filtration coefficients, diffusion coefficient, metabolic rate, (e) to determine tracer permeability in cell membranes by measurement of bulk diffusion coefficients.